This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-097552, filed Mar. 29, 2002, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a sheet size detecting device for detecting the size of sheets stored in a position.
2. Description of the Related Art
Copying machines, printers or facsimile machines have a function of detecting the size of sheets stored in a predetermined position. The sheet size detection is realized by optical sensors that are selected or used in accordance with the size of sheets. The sensors are made to detect a sheet, for example when a platen cover is closed.
Jpn. Pat. Appln. KOKAI Publication No. 6-64781 discloses a technology wherein eight sheet sizes are detected by use of three sensors. According to this publication, the sheet sizes are detected by providing guides that can be adjusted in position in accordance with a size of a sheet, providing three code plates that are movable in synchronism with the guides, and arranging three sensors that detect the code plates, respectively. When sheets are stored in a tray and the guides are moved in accordance with the sheet size, a check is made to see whether or not the three sensors detect the corresponding code plates, and the sheet size is detected based on this check. To be more specific, the sheet size detection is performed as follows. For example, when the code plates are adjusted in position to increase the size from xe2x80x9csize 1xe2x80x9d to xe2x80x9csize 8xe2x80x9d in turn, a check is made to see whether the sensors detect the sheets. The detected states of the sensors are determined by comparing the detection signals with eight bit combination patterns, which are determined beforehand and correspond to different bit information of different sheet sizes.
Since the sheet size detecting device employs sensors in accordance with the number of sheet types, a large number of sensors are required. For example, if the sheet size detecting device detects eight types of sheets, eight sensors are required. Due to the necessity of using a large number of sensors, the sheet size detecting device is inevitably large in size and costly.
In the sheet size detecting method of Jpn. Pat. Appln. KOKAI Publication No. 6-64781, three code plates and three sensors are required for detecting eight sheet sizes. That is, the bit generation means and the bit detection means must be equal in number.
Accordingly, an object of the present invention is to provide a sheet size detecting device which can detect sheet sizes by means of a compact structure, and which can be provided at low cost.
A sheet size detecting device according to one aspect of the present invention comprises: a tray in which sheets are stored; guides that can be adjusted in position in accordance with the size of sheets stored in the tray; and bit generation sections that are moved in synchronism with movement of the guides. The device detects bits based on the movement of the bit generation sections, and the number of bits detectable is larger than the number of bit generation sections by at least one. The device detects the size of sheets stored in the tray based on the correspondence between the combination of detected bits and the sizes of sheets that can be stored in the tray.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.